Trimming
the Impression
Trim the impression to within 7mm of the gingival margin areas such that the peripheral
border is equidistant from the occlusal plane in both the posterior and anterior areas, as
well as the left and right sides. This will provide a model which is equal in height
throughout the arch. On upper impressions, trim the palate to a height level with
the labial and buccal borders. Take care that the pontic areas are not left too thin. Mark
the centre line onto the impression. To identify the correct position of the impression in
relationship to the tray, place the impression face down onto the open Krystal tray and
view it through the tray base. |
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Model Release
Spray
To ensure ease of removal of the set model, spray the inside of the Krystal Tray and all
surfaces of the Orange Casting Tongue with SnapSlip Model Release Spray. Shake the spray
can before use and apply a thin even coat from a distance of about 250mm. |
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Orange Casting
Tongue
Fully insert an Orange Casting Tongue into the Krystal Tray. The Orange Casting Tongue is
used to compensate for the eventual expansion of the die stone during the setting process.
With a lower impression that has a lingual space, or if the impression does not have a
complete centre, ie no palate, block this area with SnapBlok putty so as to form a flat
smooth area; in addition, SnapBlok can be placed around the heels of the impression. The
use of SnapBlok will greatly reduce trimming time and also the amount of die stone used. |
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Pouring the
Impression
Fill the impression with die stone in the usual manner. Fill the Krystal Tray
with die stone level with the top edge of the Orange Casting Tongue and the inner border
of the tray. Do not over fill the Krystal Tray or the impression as it increases the
amount of die stone used as well as the time necessary for trimming the model. A small
amount of die stone on top of the Orange tongue is not of consequence. Invert the
impression onto the Krystal tray and position it so that the anterior teeth are placed
centrally between the tip of the Orange tongue and the outer face of the tray and also
that the midline of the impression is in line with the midline of the Orange tongue.
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Smoothing the
Model
To reduce the time necessary to trim set models it is advisable to smooth the model whilst
the die stone is still ‘plastic’. After the initial set of the die stone, wet a
finger and gently smooth away any excess die stone on the outer part of the Krystal Model
Tray and also contour the heels of the model. At this stage this will take seconds to
achieve and is much easier to work than completely set die stone. |
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Removing the
Sacrificial Membrane (Base of the Krystal Model Tray)
The base of the Krystal Model Tray has been so designed so as to contain the
liquid die stone during the pouring cycle and to be removed once the die stone has set.
Removal of the sacrificial membrane horse shoe shaped section, so that the base of the
model is in the same plane as the base of the Krystal Tray, will give a positive visual
check that all sections of the model had been completely reseated when replaced in the
tray, in addition, the open bottom of the tray will ensure that no debris can be trapped
to prevent correct re-seating of dies. The sacrificial membrane can easily be removed by
use of a standard wet or dry model trimmer. It is important that a good quality wheel on a
wet trimmer or a coarse abrasive band on a dry trimmer, is used. Check the condition of
your abrasive wheel or band If difficulty is encountered in removing the base of the tray.
When removing the sacrificial base to avoid creating excessive heat, and melting the
melting the plastic instead of cutting it, move the tray from side to side across the face
of the abrasive surface. |
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Removal of Orange
Working Tongue
Hold the tray and model as shown in the illustration, insert the narrow end of a SnapFree
tool into the slot under the rear edge of the tongue and using the back of the Krystal
Tray as a fulcrum gently slide the Orange Tongue out of the model. |
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| REMEMBER ! Die Stone
Expands When Setting
If you leave
the model in the tray too long it will be more difficult to remove ! |
Model Removal from
the Krystal Tray
Remove the impression from the model in the usual manner. Hold the Krystal Model Tray as
shown in the illustration, that is holding the model with the thumb and fore finger as
shown, and supporting the underneath of the tray with the other fingers, gently tap the
centre of the Krystal Model Tray with the nylon end of the SnapTap mallet, then gently tap
the angled outer corners of the tray as shown. Do NOT use excessive force, this is not
necessary and may damage the model. Repeat this process until the model releases from the
tray.
Using your fingers, remove any slight amount of flash, excess die stone or SnapBlok which
may be around the model. Where necessary trim the model by using a router or arbor band in
a handpiece. |
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| Sawing the
ModelUsing a
fine separating saw blade - saw through the model to separate the preps and pontics. |
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| NEVER leave
excessively long model segments - their percentage expansion will cause problems when re-seating the
model into the tray.
This model segment is too long and will cause
problems particularly when the model is used for a single unit ! The simple solution is to make
additional saw cuts. |
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| An extra saw cut has been
made in the model to reduce excessive segment length. This method allows for a more even
expansion of the whole model and helps to avoid re-seating problems.
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Rremove any model dust and
replace the sections into the Krystal Model Tray. Hold the tray and the model sections
from above and give the base of the tray a short, sharp, knock on the worktop to settle
the model sections and to ensure that all the sections are fully seated.
Insert a WHITE working tongue into the Krystal Model Tray to securely retain all of the
model sections back in their original positions. The ease of fitting and removal of the
tongue depends on the expansion of the model stone used. |
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| To subsequently remove all
the model sections from the tray, remove the white working tongue, place the
ejector/articulation plate on the bench top so that the shaped segments are facing
upwards. Place the tray on top of the plate so that the shaped segments are located
adjacent to the openings in the bottom of the tray. Push down firmly on the tray and the
segments will be released from the tray. Single sections can be easily pushed out by hand
from underneath. |
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